1. Field of the Invention
The present invention relates to a wiring board, method for manufacturing a wiring board and an electronic component using a wiring board, and more specifically to a wiring board, method for manufacturing a wiring board and an electronic component using a wiring board that can provide a small and thin passive component such as solid condenser, resistor, coil, transistor or so on.
2. Prior Art
Up to now, a passive component such as capacitor or resistor together with a semiconductor chip such as CPU (Central Processing Unit) or memory has been used in an electronic equipment, and an electronic component using a chip type condenser element has been used as the capacitor. A tantalum solid electrolytic condenser element is mentioned as an example of a chip type condenser element.
A tantalum solid electrolytic condenser element is provided with an anode formed by a porous sintering body manufactured by sintering high purity tantalum powder in high temperature and high vacuum atmosphere, and a dielectric formed by a tantalum pentoxide synthesized electrochemically in acidic medium. Further, a cathode is formed by a low resistivity solid electrolytic layer such as manganese dioxide or conductive polymer, a carbon layer and a silver layer.
Since a tantalum solid electrolytic condenser element has large electrode area by using a porous anode, it is suitable for miniaturization and enlarging capacity of components. Further it has excellent alternating characteristic and high reliability by using a solid electrolyte as a cathode. Therefore, a chip type condenser using a tantalum solid electrolytic condenser element has been used as a capacitive component of a mobile communication equipment such as a portable telephone or a portable electronic equipment such as a notebook personal computer requiring small size, thin shaping, high frequency and large electric current capacity.
Moreover, a chip type condenser was formed by connecting a tantalum solid electrolytic condenser element on a lead frame and encapsulating around the tantalum solid electrolytic condenser element with resin. However, it becomes difficult to increase a static capacitance comparing with external size because of recent miniaturization and thin shaping of electronic equipment. To solve these problems, a chip type condenser which does not use lead frame is proposed by Japanese unexamined patent publication number 08-148386 or 2001-307946.
A chip type condenser mentioned in Japanese unexamined patent publication number 08-148386 comprising, as shown in FIG. 1, a condenser element 3 provided with a anode 301, cathode 302 and dielectric 303, an insulating board 1 provided with a first supporting portion 1B supporting the anode 301 of the condenser element 3, a second supporting portion 1C supporting the cathode 302 of the condenser element 3, and a first external terminal 9 and a second external terminal 10 formed respectively on bottom of the first supporting portion 1B and the second supporting portion 1C and connected respectively with the anode 301 and the cathode 302 through conductive substance 11 and 12, and a case 13 covering main portion including the condenser element 3 supported by the insulating board 1.
A chip type condenser mentioned in Japanese unexamined patent publication number 2001-307946 using, as shown in FIG. 2, a stereoscopic wiring board provided with recessed portion 14 and stepped portion 15. The stepped portion 15 is formed by the insulating board 1 and resin 23, 25 laminated both sides of the insulating board 1. The recessed portion 14 is a portion where the condenser element 3 is mounted. Upon the stepped portion 15, a conductor 16 used as an anode is provided, and corresponding to the conductor 16 an anode terminal 17 is provided on the rear surface of the stereoscopic wiring board. A conductive layer 18 used for cathode is provided on the bottom surface of the recessed portion 14, and corresponding to the conductive layer 18 a cathode terminal 19 is provided on the bottom of the stereoscopic wiring board. The conductor 16 used as an anode and the anode terminal 17 are connected by a conductor 20 provided within a connecting hole 24, and the conductive layer 18 used as a cathode and the cathode terminal 19 are connected by a connecting hole 27. Numeral 26 denotes resin filled in the connecting hole 24.
Further, the condenser element 3 is mounted to the recessed portion 14, and the anode 301 is placed on the stepped portion 15 and connected to the conductor 16 used as an anode. The cathode 302 is connected with the conductive layer 18 used as a cathode through conductive adhesive agent 4B.
However, in the conventional wiring board used for the chip type condenser, the external terminal is provided on the bottom of the insulating board, namely on the side bottom of the plane where the condenser element is connected, and the external terminal is connected with the anode and cathode of the condenser element through the conductor formed within the through hole provided to the insulating board.
Plating or filling a conductive resin is considered as a method for forming the conductor within the through hole provided to the insulating board, but it becomes difficult to fill conductive material within the through hole, because diameter of the through hole is getting small according to recent miniaturization of chip type condenser. Accordingly, conductive imperfection is apt to occur due to imperfect filling of conductive material within the through hole.
Further, since conductive imperfection is apt to occur within the through hole, miniaturization of the chip type condenser becomes difficult because of difficulty of further miniaturization of the wiring board.
In a chip type condenser mentioned in Japanese unexamined patent publication number 08-148386, forming of conductive substance 11, 12 within the through hole 11A, 12A is difficult, because the depth of the anode 301 side through hole 1A is different from the depth of the cathode 302 side through hole 12A.
Further, in a chip type condenser mentioned in Japanese unexamined patent publication number 08-148386 and 2001-307946, since the stepping portion is formed to connect the anode of the condenser element and the conductor used as an anode on the insulating board, manufacturing cost is risen by increasing manufacturing process of the wiring board for use in the chip type condenser.